In recent years, it has become increasingly more desirable to be able to integrate more than one semiconductor laser into a single optical device. For example, various different optical disc formats such as compact disc (CD), digital versatile disc (DVD) and Blu-ray Disc™ have become popular for recording digital data and entertainment. Nevertheless, each of these optical disc formats requires a different wavelength of semiconductor laser for its implementation. Therefore, forming an optical disc drive capable of reading and writing to more than one format of optical disc requires that two or more semiconductor lasers be included in a single optical disc drive.
What is more, laser printers typically utilize a single semiconductor laser to form images on a photoreceptor drum so that the images can subsequently be transferred to paper. The speed that a laser printer can print a page is generally a function of the output power of its semiconductor laser. The higher the laser output power, the faster the print speed. As a result, it is advantageous to combine the output powers of more than one semiconductor laser in a laser printer in order to increase print speed.
An optical device such as an optical disc drive or laser printer typically uses a set of steering optics to direct the output of its semiconductor laser to its respective target (e.g., optical disc media or photoreceptor drum). Such steering optics may comprise, for example, fixed and movable mirrors, prisms, gratings and lenses. In those optical devices where more than one semiconductor laser is to be employed, it is generally beneficial to have a single set of steering optics for all of the semiconductor lasers rather than a separate set of steering optics for each semiconductor laser. Having a single set of steering optics substantially reduces the complexity, size and cost of the optical device.
Implementing a single set of steering optics in a multi-laser optical device usually necessitates that the laser beams for the multiple lasers be brought into close proximity with one another and directed in substantially the same direction so as to mimic a laser beam emitted from a single laser source. For implementing two semiconductor lasers in a single optical device, U.S. Pat. No. 6,038,204, entitled “Optical Source Module for Generating Beams with Different Wavelengths,” for example, describes a laser assembly comprising a silicon substrate having a patterned feature with a triangular cross-section located between two opposing semiconductor lasers that are mounted to the substrate. The laser beams of the two opposing semiconductor lasers are reflected by the oblique surfaces of the patterned feature so that the reflected laser beams approximate the light emitted from one laser. Nevertheless, despite the apparent simplicity of such a design, it is typically very difficult to pattern a triangular feature in a silicon substrate with oblique angles oriented 45 degrees in relation to the surface of substrate using conventional silicon substrates and processing techniques. Thus, such a laser assembly does not easily lend itself to mass production. In order to address this difficulty, U.S. Pat. No. 6,937,405, entitled “Optical Pickup Projecting Two Laser Beams from Apparently Approximated Light-Emitting Points,” suggests positioning a discrete cube of silicon between two opposed semiconductor lasers such that the laser beams from the two semiconductor lasers reflect off two surfaces of the cube at 45 degree angles. Of course, such a solution adds considerable complexity and expense to the formation of the laser assembly. Moreover, neither one of the above solutions readily allows the optical coupling of the outputs from more than two lasers.
As a result, there is a need for a laser assembly that allows the laser beams from two or more lasers to approximate a laser beam emitted from a single laser source without the attendant disadvantages found in the prior art.